Hollis,
Although I have only been diving a Prism for a year now, I love my unit and have some very definite comments on your post regarding the new Prism 2 and the direction you should pursue.
First and foremost, you should consider the rig a TECHNICAL rebreather and not bother with all the recreational BCD stuff. As soon as I got my Prism home, the BCD was completely removed and the DSS "Prism 6 bolt to 2 bolt adapter plate" was installed as well as their "Counterlung yoke adapter". This allowed me to ditch the BCD in favor of a stock backplate and wing (I use the Agir 38lb which is perfect for the Prism).
Silent Running, Andy
Thank you for the post, questions, and testimonial!
In working on the re-engineering of the Prism, our first objective is to bring all the wonderful aspects of Peters Prism forward, with slight changes, to allow us to manufacturer the Prism more efficiently.
Our determination to do this with Peters Prism is in a large part based on input from divers like you who have a depth of experience in open circuit systems. Time and again we have been told of the durability of the Prism, and its ability to be field serviced so no dives are missed. Peter makes the excellent point about the oxygen sensor driven analog Secondary Display, that in the event of a loss of the system electronic oxygen set point control, the dive can continue as planned, just using manual control.
This puzzles me. While much in the OC world can be of value to the rebreather diver, I would not necessarily seek out just OC advice.
The Prism2 counterlungs will be attached just like the Prism counterlungs. There will be a Velcro gator and side release buckle at the top and the lower attachment will be another side release buckle that will attach to the harness waist strap, and the counterlungs will act as the shoulder strap. We will add a 2 inch D-ring on the outboard side of each counterlung at the middle of the length of the counterlung. We will retain the integral weight pocket.
Please don't go this route. The counterlungs are NOT shoulder straps, and trying to make them do double duty is a less than optimal approach, IMO. My shoulder straps are provided by the stock backplate (single webbing design). The counterlungs attach at the top to the yoke adapter, and at the bottom I use the stock Prism web between the fastex on the bottom of the CL and have the harness waistband pass through. Since that opening is rather large, I have rubber innertube loops to reduce the opening thru which the waistband passes. Works great.
Under the counterlung d-rings (again DSS) are a perfect solution. Putting D-rings on the counterlungs will put stress on the counterlungs that is totally unnecessary. Let the harness do it's job, and let the counterlungs do their job - please.
Regarding bail out cylinder mounting; the envisioned configuration is to clip the valve to the D-ring on the outboard side of the counterlung and the lower attachment point is a D-ring mounted where the waist strap meets the backplate. From looking at Jill Heinerths video about side mounting on a rebreather, the Prism2 would be adaptable to that system too. We agree with you regarding drag, streamlining, and ease of use. Also comfortable, efficient, and enjoyable are all good words to use in safe dive equipment design.
Again, please just let the counterlungs be counterlungs. Let the harness /backplate do it's job.
As for sidemount, once you have a harness/backplate, you can easily add sidemount to it, so there's no need to worry about it in the Prism 2 design (unless you want to do all this tomfoolery about the counterlungs and D-rings and such).
We are going to change the waist strap to 2 inch webbing, with an optional cummerbund, and some pocket options including ditchable weight pockets, similar to the waist harness on the Hollis HTS. Based on input from Tech divers we will be using a crotch strap, rather than the thigh straps the original Prism uses, but the system will adapt to thigh straps. We are working on a design that will allow lots of customization. We should have this done in 6 weeks or so. We are also investigating an adapter to allow the use of tech metal backplates; we will have to revisit the counterlungs so they can be attached to the backplates shoulder straps.
Again - why not just ditch all this nonsense and provide a proper mount point (i.e. two bolts) for a backplate and wing of the owner's choice? You could supply one with the unit (most backplate/harnesses are pretty much the same from various vendors) and a good small (38lb) wing. (Whether you go donut or horseshoe is one of those "mine's better than your's debates anyway).
We are working on tweaking the BC. Our concerns echo yours; we want great balance for horizontal trim, and a BC that is not going to get pinched when the Prism2 is placed on a bench in a vertical orientation for donning.
AGAIN... a stock harness/backplate/wing will provide this without Hollis wasting time reinventing the wheel. This bit of the kit has pretty much been refined by now - just use something classic and proven.
We like the analog Secondary Display too. We have a design effort underway to develop a battery powered digital Secondary Display, and we will continue to make the oxygen sensor powered analog Secondary Display that you like. It is indeed impressive to hear divers discuss an electronic mixed gas rebreather where a failure in the electronics is no big deal.
That is good news.
We are keeping an eye on servicing the Prism2 during our redesign efforts. We expect to deliver the Prism2 with most items user serviceable, and some items would require returning to a competent service facility, and some items would require returning to the factory. Most items can be swapped out; we will have spares readily available. Replacing some items, like the solenoid, would require access to the electronics housing, not something done casually. Calibration of the depth transducer would require specialized equipment, and would probably require returning the Prism2 scrubber head/electronics housing to the factory or specially set up service center.
I agree with a prior post - there is no reason the solenoid could not be user replaceable. The Prism currently uses molex connectors for the cells, so something similar could be inside the head for the solenoid.
We are planning on an optical data out port to transmit real time PPO2 to a dive computer. We are also planning for onboard logging of time, depth, and PPO2. We will have download of this data by USB, just like a dive computer with a PC application to save and display the data graphically and in analog mode. We do not want to disclose the algorithms we are considering at this time, one is new and revolutionary, one is established and well tested. It would not be too hard to make a black box that would convert the optical output PPO2 to a voltage value that would mimic an oxygen sensor.
OK. Don't really care, but these type of options are common in most rebreathers now, so you have to offer them or risk being labeled "dinosaur". I prefer tables, a bottom timer and a brain, but others will have different desires and choices.
We plan to have comfortable carrying handles on the top and bottom of the Prism2. One change from the Prism is where the cables plug in. We will use 90° fittings on the cables to attach to receptacles on the bottom of the electronics housing. This will let us rout the cables away from the carrying handle. With the exception of the cable to the Secondary Display the other cables will be well protected.
Sounds OK. I have not had any problems with the cables or attachments, so I'm not sure this is really a big item, but if it improves routing without introducing a failure point, that's alright. Mind you, I've never had good luck with ANYTHING electronic and a 90 degree connector, but who knows - you might be the one to get that right. ;-)
In regards to scrubber duration, the 255 minutes (4 hours, 15 minutes) was the average of several runs done by the NEDU in Panama City. The dives we done with an injection rate of 1.35 SLPM of CO2, a RMV of 40, water temperature of 40 F, at 60 FSW. The time given is the time it took to reach 0.50% CO2 SEV. Scrubber duration is very dependant on depth, water temperature, work load, and varies lot to lot of scrubber material. Shallow warm water where the diver is just observing marine life will yield the longest time, and deep cold dives swimming into a strong current will yield the shortest duration. The 245 minutes looks like a typo, thanks for pointing it out.
As long as you don't make major changes to the current radial scrubber or the technologies that keep the scrubber away from the small amounts of moister in the bucket, and still provide the duration, that's good.
We have all of the injection molded components for the breathing loop in hand and are working with our suppliers to correct minor non-conformities in the components. The design package will be finished this week, which is delaying our schedule to build the first Prism2. With luck we will assemble a Prism2 in the later part of July or early August. Then the testing begins.
Hollis
Sounds good. Please post some pictures of a unit AFTER you have done the first dive or two on it. I'm looking forward to seeing the new unit.
ONE OTHER THING - it would be nice to offer the unit in two configurations - "ready to go" (that is, with wing, backplate and harness) and "almost ready to go" (no backplate, wing or harness but ready to attach to one of the purchaser's choice).
Cheers,
-S